Fluidic input isolation circuit

ABSTRACT

A FLUIDIC CIRCUIT CONNECTED AT THE INPUT TO A FLUIDIC SYSTEM PERMITS A PULSATING FLUID PRESSURE SIGNAL CONTAINING HARMFUL CONTAMINANTS TO BE UTILIZED IN A FLUIDIC SYSTEM. THE INPUT CIRCUIT ISOLATES THE FLUIDIC SYSTEM FROM A CONTAMINATED OR HIGH TEMPERATURE FLUID SIGNAL SOURCE BY PROVIDING A REVERSE FLUID FLOW IN AN INPUT FLUID PASSAGE WHICH, HOWEVER, TRANSMITS THE INFORMATION BEARING PULSATING PRESSURE SIGNAL TO THE FLUIDIC SYSTEM. THE ISOLATION CIRCUIT CONSISTS OF A SOURCE OF NONCONTAMINATED, PRESSURIZED FLUID CONNECTED THROUGH A FLUIDIC RESISTOR TO THE INPUT FLUID PASSAGE. THE SOURCE OF NONCONTAMINATED FLUID IS AT A SUFFICIENTLY HIGH PRESSURE TO ASSURE THE REVERSE FLOW UNDER ALL OPERATING CONDITIONS OF THE FLUIDIC SYSTEM. AN OPTIONAL FLUIDIC DECOUPLING CIRCUIT CONNECTED AT THE OUTPUT OF THE ISOLATION CIRCUIT CONVERTS THE SIGNAL-SIDED SIGNAL TO A PUSH-PULL SIGNAL.

United States Patent [72] Inventor Martin C. Doherty Scotia, N.Y.

211 App]. NO. 808,952

[22] Filed Mar. 20, 1969 [45] Patented June 28, 1971 [73] Assignee GeneralElectricCompany [54] FLUIDIC INPUT ISOLATION CIRCUIT 15 Claims, 2 Drawing Figs.

3,489,009 I/l970 Rimmer 3,489,014 l/l970 Przybylko 137/81.5X l37/81.5X

ABSTRACT: A fluidic circuit connected at the input to a fluidic system permits a pulsating fluid pressure signal containing harmful contaminants to be utilized in a fluidic system. The input circuit isolates the fluidic system from a contaminated or high temperature fluid signal source by providing a reverse fluid flow in an input fluid passage which, however, transmits the information bearing pulsating pressure signal to the fluidic system. The isolation circuit consists of a source of noncontaminated, pressurized fluid connected through a fluidic resistor to the input fluid passage. The source of noncontaminated fluid is at a sufficiently high pressure to assure the reverse flow under all operating conditions of the fluidic system. An optional fluidic decouplingcircuit connected at the output of the isolation circuit converts the single-sided signal to a push-pull signal.

FLUIDIC INPUT ISOLATION CIRCUIT My invention relates to a fluidic circuit for isolating a contaminated or high temperature fluid source from the input to a fluidic system while transmitting a pulsating pressure information signal from such source to the fluidic system for utilization thereby.

Fluidic systems are highly reliable because of their inherent lack of moving mechanical parts which would be subject to wear and eventual failure. However, this reliability is greatly reduced unless all fluids introduced into the fluidic circuitry are very highly filtered and free of contamination, and at a sufficiently low temperature consistent with the material of which the fluid amplifiers and other elements of the fluidic circuitry are fabricated.

In some fluidic control system applications, it is very convenient to utilize particular pressure signals, but contamination or excessively high temperature of the fluid medium on which the signals are impressed precludes the use of such signals. An example of such application is a fluidic speed governor for controlling the speed of hydraulic and pneumatic machines of the positive displacement type, such as air motors, wherein the machine speed can be sensed directly from pressure pulsations generated in the machine housing, supply and exhaust lines due to the reaction of the motion of sliding vanes, rotors, pistons or gear teeth on the fluid passing through the machine. This fluidic speed governor is described and claimed in my concurrently filed Pat. application Ser. No. 808,869 entitled Fluidic Speed Governor," and assigned to the assignee of the present invention.

The fluid in the above-described machine housing, supply and exhaust lines generally contains contaminants such as oil in the case ofa pneumatic machine, or may be at an excessively high temperature thereby precluding its use as a control signal medium. The fluid from this contaminated or high temperature source, if permitted to enter the fluid circuitry would cause contamination and, or, improper operation of the fluidic system. The contaminating particles of oil could cause partial or total blockage of fluid amplifier control nozzles and fluidic resistors. The excessively high temperature could cause failure of the materials of which the fluidic circuitry is fabricated, and even moderate temperatures of less than 1,000 F. are undesirable since the capacitance of fluidic capacitors utilized in the fluidic circuitry is a function of absolute temperature.

It is obvious that the mere use of a filter might capture particles of appropriate size in the contaminated fluid but would probably wash out the pressure pulsating signal and would not prevent the oil contamination or high temperature from passing to the fluidic circuitry.

Therefore, one of the principal objects of my invention is to provide a fluidic isolation circuit for preventing contaminated or high temperature fluid from entering a fluidic system.

Another object of my invention is to provide such isolation circuit whereby a pulsating pressure signal in the contaminated or high temperature fluid is transmitted to the fluidic system.

A further object of my invention is to provide a fluidic circuit for converting a contaminated or high temperature singlesided pulsating pressure signal to a noncontaminated or low temperature push-pull pulsating pressure signal.

Briefly stated, and in accordance with the objects of my invention, I provide a fluidic circuit at the input of a fluidic system which isolates a contaminated or high temperature pressurized fluid signal source from the fluidic system, but transmits a pulsating pressure signal, which is impressed on the undesired fluid, to the fluidic system for processing thereof. The isolation circuit consists of a source of noncontaminated, low temperature, relatively constant pressurized fluid connected through a fluidic resistor to an input passage which transmits the pressure pulsating fluid signal to the fluidic system. The source of noncontaminated fluid is at a sufficiently high pressure to assure reverse fluid flow through the input passage to thereby prevent the undesired contaminated or high temperature fluid from entering the fluidic system while permitting the pulsating fluid signal to pass therethrough. A decoupling circuit including a fluid resistor in a first passage, and a fluidic resistor and reactive element in a second passage is connected between the output of the isolation circuit and the fluidic system for converting the singlesided signal to a push-pull signal.

The features of my invention which I desire to protect herein are pointed out with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the accompanying drawing, wherein like parts of the several FIGS. are identified by the same reference character, and wherein:

FIG. 1 illustrates a first embodiment of my invention for obtaining a single-sided control signal; and

FIG. 2 illustrates a second embodiment of my invention for obtaining a push-pull control signal.

Referring now in particular to FIG. 1, there is shown a first embodiment of my invention which is especially adapted for providing a noncontaminated and relatively low temperature single-sided pressure pulsating fluid signal to a fluid amplifier circuit. My invention, a fluidic isolation circuit designated as a whole by numeral 11, is connected into a control fluid inlet line 12, 14 which connects a pressure pulsating fluid signal source 13 to the input of a particular fluidic circuit in a fluidic system, the input generally including a fluidic resistor R,. For the purposes of this invention, source 13 consists of a steadystate (DC) pressurized, contaminated or high temperature fluid on which an information signal is impressed in the form of pressure pulsations (an AC component). The DC pressure of the fluid in source 13 is sufficiently high such that the direction of fluid flow would tend to be from source 13 to resistor R,. Source 13 is any fluid flow passage or device in which a contaminated or high temperature pressurized fluid flows or is contaminated, and an information signal in the form of a variable frequency or repetition rate pressure pulsation is impressed on the steady-state pressure of the fluid wherein the pulsation frequency or repetition rate is directly proportional to the magnitude of a parameter being sensed by the fluidic system. A typical example of such contaminated or excessively high temperature fluid signal source is the machine housing, supply or exhaust line of hydraulic and pneumatic machines of the positive displacement type hereinabove described wherein the pressure pulsation frequency or repetition rate is directly proportional to the machine speed.

My input isolation circuit consists of fitting 11a, a source of noncontaminated, relatively low (and generally ambient) temperature, relatively constant pressurized fluid P,,, a fluidic resistor R and suitable tubing 11b, 110, for interconnecting resistor R between fitting 11a and supply P, Fitting lla provides the connection of my isolation circuit into inlet line l2, 14. The pressure of supply P, is selected to be considerably greater than the pressure of the contaminated fluid in source 13, and the combination of the pressure of supply I, and the resistance value of resistor R are selected to obtain a pressure level at fitting 11a which is also considerably greater than the pressure in source 13 to assure a reverse flow of fluid through passage 12 which connects fitting 11a to source 13. The pressure pulsation (AC) signal, however, is transmitted through passage 12 (and 14) since the AC fluid resistance of source 13 is much greater than the DC resistance (to the steady-state pressure). 1

Source P, is, in many instances, the pressurized fluid source which provides power fluid supply pressures at substantially ambient temperature to various fluid amplifiers in the fluidic system. Resistor R is a fluid flow restrictor such -as a nozzle, sharp-edged orifice, capillary section, or a variable resistor device of the type described in copending application Ser. No. 679,771, filed Nov. 1, 1967, inventors Vogelsang et al., and assigned to the assignee of the present invention. The purpose of resistor R 'is to isolate the pulsating pressure signal from power supply P,, and the resistance value thereof is sufficiently small so that the pressure of the noncontaminated fluid at fitting 11a is still substantially greater than the pressure of the contaminated fluid in source 13. Tubing sections 11b and 11c which connect the ends of resistor R to fittinglla and supply P respectively, as well as all of the other fluid flow lines and passages herein disclosed, may be of the flexible or nonflexible type and manufactured of a material suitable for the particular application, typical examples of tubing material being plastic, rubber, copper, stainless steel, and the like. The inner diameter of tubing sections 1l-b and 110 is not critical and is merely of such size to assure adequate fluid flow from supply P, to fitting 11a and passage 12 to reverse the flow of contaminated fluid tending to flow in passage 12. Alternatively, fitting 11a, resistor R and tubings llb, 11c may be part of an integral laminated structure which includes the fluidic circuitry, in which case tubing sections 11b and He would merely be apertures formed through one or more laminates which provide communication of supply P, with a first end of resistor R and communication of the second end of resistor R with passages 12 and 14. The input end of passage 12 is connected to source 13 by means of a suitable fitting 15. As a typical example, fittings l and 110 may be conventional T couplers fabricated of materials appropriate for the tubings being interconnected thereby such as plastic, copper and the like. Alternatively, fitting may be of a more simple type such as the threaded fitting 15 in FIG. 2 which merely provides an opening in the wall of line 13.

In a typical example of utilization of my fluidic isolation circuit at the input of the above-referenced fluidic speed governor, contaminated or high temperature signal source 13 is the exhaust line of an air motor. It will be assumed that the steadystate (DC) pressure level of the contaminated fluid flowing in exhaust line 13 is approximately 0.4 p.s.i. gauge and the AC component (peak-to-peak pressure pulsation amplitude) is approximately 0.1 p.s.i. gauge as indicated in the waveform at the input end of line 13. The amplitude of the pressure pulsations is variable within relatively small limits whereas the steady-state pressure level is variable over a wide limit as determined by the speed and load on the pneumatic or hydraulic machine to which exhaust line 13 is connected. Thus, supply pressure P, and resistors R are chosen to assure reverse flow through tubing 12 at the worst conditions of the governed machine operation (the highest DC pressure level of fluid in line 13 which generally corresponds to rated speed and rated load conditions). The fluid employed in my isolation circuit is a gas such as air in the case of pneumatic machine applications, and a liquid such as oil in the case of a hydraulic machine speed governor application. The inner diameter of the tubing 14 which is connected between fitting 11a and the input of the fluidic system is determined primarily by the fluid circuitry and is generally in a range of one-tenth to one-fourth inch. For the example wherein the DC pressure level of contaminated fluid in line 13 is approximately 0.4 p.s.i., the pressure of supply P is approximately 1.8 p.s.i. and the resistance value of resistor R is approximately 1,000 seconds/inch such that the pressure at fitting 11a is approximately 1.5 p.s.i., all pressure being gauge. For this resistance value of R the resistance of R would typically be approximately twice such value.

The embodiment of my input isolation circuit illustrated in FIG. 1 develops a single-sided signal in tubing 14 (indicated by an appropriate waveform) which preserves the (0.1 p.s.i.) pulsating pressure signal present in line 13 but which is now impressed on a noncontaminated, low temperature fluid having a (1.5 p.s.i.) DC pressure level higher than that in line 13. In many applications, however, the first stage of fluidic circuitry of the fluidic system for which my invention provides input isolation comprises a proportional type fluid amplifier having oppositely disposed control fluid nozzles to which are supplied the pulsating pressure signal in push-pull or differential pressurized form. The FIG. 2 embodiment of my invention is utilized to obtain the push-pull signal from source I3.

Referring now in particular to FIG. 2, there is shown a proportional type fluid amplifier 22 comprised of a power fluid nozzle supplied from source P opposed control nozzles 20, 21 and fluid receivers 23, 24 downstream of the power nozzle. Control nozzles 20 and 21 are supplied with the pressure pulsating signal fluid through passages 26 and 28, respectively. The input ends of passages 26, and 28 are connected to a conventional fitting 27 which has its input connected to the out put end of passage 14. A decoupling circuit in the control fluid inlet passages 26, 28 consists of a first fluid flow restrictor R connected in passage 26, and a second fluid flow restrictor R and fluidic capacitor C connected in passage 28. The two restrictors R R are of equal dimension to provide equal re sistances to fluid flow therethrough. Capacitor C may be a fixed volume for pneumatic applications or a hydraulic accumulator for hydraulic applications. This decoupling circuit constituted by passive fluidic elements R R and C is briefly described in my aforementioned concurrently filed patent application, and is described in detail in U.S. Pat. No. 3,400,729 to Boothe and assigned to the assignee of the present invention. Briefly, the R C resistance-capacitance circuit (or a re sistance-inductance circuit) in the control fluid inlet passage 28 of amplifier 22 delays the response in such control inlet to transient fluid pressure signals such as the pressure pulsation signal passing through tubing 14 to amplifier 22. The transient signal, of course, passes through control inlet passage 26 without any delay. The time constant T of the R-C (or R-L) circuit in control passage 28 is sufficiently large that the corresponding frequency. l/T is approximately one-tenth of the lowest frequency i-n the normal operating frequency range of the fluidic system which amplifier 22 constitutes the input stage. Thus, with reference to the attenuation versus frequency characteristics FIG. 3 of the Boothe U.S. Pat. No. 3,400,729, the R C values are chosen such that the break frequency separating frequency ranges A and B is at a sufficiently low frequency whereby the decoupling circuit operates in the higher frequency range B wherein any change in the signal pressure amplifier 22 is solely dependent on amplitude changes in the pressure pulsation signal sensed in line 13. The waveforms and approximately pressure amplitudes of the DC level and AC signal at the input (signal source 13) and output (receivers 23, 24) are illustrated in FIG. 2 for a typical application. The decoupling circuit thus converts the single-sided input signal into a push-pull or differential pressurized signal (two identical signals which are 180 out of phase) of the same frequency or repetition rate as the single-sided signal. The resistors R,, R cause a slight attenuation of the AC signal, but the gain of first stage amplifier 20 recovers any decrease in signal amplitude caused by the resistors. As a typical example, for the case of a fluidic system having a normal operating frequency range of approximately -13 1,500 Hertz, the values R C are chosen to obtain a break frequency of approximately 60 Hertz and a corresponding time constant T=R C of approximately 0.003 seconds. The output of proportional amplifier 22 is generally connected to the control fluid inlets of another proportional type fluid amplifier which may provide further amplification of the AC component of the input signal or another type of processing of such signal.

From the foregoing description, it can be appreciated that my invention makes available a new fluidic circuit which is adapted for isolating the input to a fluidic system from contaminated or high temperature fluid having a pressure pulsating signal impressed thereon. My input isolation circuit has the distinct advantage of having no moving mechanical parts which would be subject to wear or improper operation. Having described my invention, the scope thereof is defined by the following claims.

I claim:

1. A fluidic isolation circuit for isolating the input of a fluidic system from the contaminated or high temperature fluid in a fluid pressure pulsation signal source and permitting the pressure pulsation signal to be transmitted to the fluid system, comprising;

a source of noncontaminated, relatively low temperature fluid of pressure magnitude greater than the steady-state pressure of contaminated or high temperature fluid in a fluid pressure pulsation signal source;

a first fluidic resistor;

means for connecting a first end of said first resistor to said source of noncontaminated, low temperature fluid, and for connecting a second end to ajuncture with a passage means interconnecting the fluid pressure pulsation signal source to the input of a fluidic system which processes the pressure pulsation signal;

the pressure of said source of noncontaminated, low temperature fluid and the fluid flow resistance of said first resistor having selected values to assure reverse fluid flow through the passage means whereby the contaminated or high temperature fluid is prevented from entering the fluidic system while the pressure pulsation signal is trans mitted thereto; and

means in communication w-ith the passage means and fluidic system input for converting the pressure pulsations from a single-sided signal to a differential pressured pulsating signal.

2. The fluidic isolation circuit set forth in claim 1 wherein said passage means comprises:

a third passage comprising a first control fluid inlet of a proportional type fluid amplifier;

a fourth passage comprising a second and opposed control fluid inlet of the proportional type fluid amplifier;

said third and fourth passages having a common juncture at input ends thereof in communication with said juncture of the second end of said first resistor and said passage means; and

said converting means comprise:

a second fluidic resistor provided in said third passage;

and

a third fluidic resistor and a fluidic reactive element in a series circuit relationship therewith for determining a time delay circuit provided in said fourth passage, the frequency corresponding to the time constant of the delay circuit being less than the minimum frequency of pressure pulsation in the signal source.

3. The fluidic isolation circuit set forth in claim 2 wherein said fluidic reactive element comprises a fluidic capacitor.

4. The fluidic isolation circuit set forth in claim 2 wherein the resistance values of said second and third fluidic resistors are equal;

5. The fluidic isolation circuit set forth in claim 2 wherein the resistance value of said first resistor is less than the resistance of said second resistor.

6. A fluidic isolation circuit for isolating the input of a fluidic system from the contaminated or high temperature steady-state pressure fluid in a fluid pressure pulsation signal source while transmitting to the fluidic system a fluid pressure pulsation signal wherein the pressure pulsation frequency is directly proportional to the magnitude of a parameter being sensed by the fluidic system, comprising:

a source of noncontaminated, ambient temperature fluid of pressure magnitude greater than the pressure of contaminated or high temperature fluid in a fluid pressure pulsation signal source comprised of a steady-state pressure and single-sided pressure pulsation signal impressed thereon;

a first fluidic resistor;

first passage means for connecting a first end of said first resistor to said source of noncontaminated, ambient temperature fluid, and for connecting a second end of said first resistor to a juncture with a second passage means which connects the fluid pressure pulsation signal source to the input ofa fluidic system which processes the pressure pulsation signal;

the pressure of said source of noncontaminated, ambient temperature fluid and the fluid flow resistance of said first resistor having selected values to obtain a pressure at the juncture greater than the pressure of the contaminated or high temperature fluid to assure reverse fluid flow through the second passage means whereby the contaminated or high temperature fluid is prevented from entering the fluidic system while the pressure pulsation signal is transmitted thereto;

said second passage means comprises a second passage having an input end connected to the pressure pulsation signal source and a second end connected to the juncture with said first passage means;

a fitting connected at the juncture of an output end of said second passage and said first passage means for providing fluid communication between the respective passages and for providing a connection to an input end of a third passage comprising a first input to the fluidic system;

said fitting further provides a connection to an input end of a fourth passage comprising a second input to the fluidic system; and

means provided in said third and fourth passages for converting the single-sided pressure pulsation signal to a differential pressurized pulsating signal which is applied to the fluidic system.

7. The fluidic isolation circuit set forth in claim 6 wherein said converting means comprise:

a second fluidic resistor provided in said third passage; and

a third fluidic resistor and a fluidic reactive element provided in said fourth passage for determining a time delay circuit.

8. A fluidic isolation circuit for isolating the input of a fluidic system for the contaminated or high temperature steady-state pressure fluid in a fluid pressure pulsation signal source while transmitting to the fluidic system a fluid pressure pulsation signal wherein the pressure pulsation frequency is directly proportional to the magnitude of a parameter being sensed by the fluidic system; comprising:

a source of noncontaminated, ambient temperature fluid of pressure magnitude greater than the pressure of contaminated or high temperature fluid in a fluid pressure pulsation signal source comprised of a steady-state pres sure and single-sided pressure pulsation signal impressed thereon;

a first fluidic resistor;

first passage means for connecting a first end of said first resistor to said source of noncontaminated; ambient temperature fluid, and for connecting a second end of said first resistor to a juncture with a second passage means which connects the fluid pressure pulsation signal source to the input of a fluidic system which processes the pressure pulsation signal;

the pressure of said source of noncontaminated, ambient temperature fluid and the fluid flow resistance of said first resistor having selected values to obtain a pressure at the juncture greater than the pressure of the contaminated or high temperature fluid to assure reverse fluid flow through the second passage means whereby the contaminated or high temperature fluid is prevented from entering the fluidic system while the pressure pulsation signal is transmitted thereto;

said second passage means comprises a second passage having an input end connected to the pressure pulsation signal source and a second end connected to the juncture with said first passage means;

a fitting connected at the juncture of an output end of said second passage and said first passage means for providing fluid communication between the respective passages and for providing a connection to an input end of a third passage; and

a second fitting connected at the output of the third passage for coupling the output end of said third passage to input ends of fourth and fifth passages wherein said fourth and fifth passages comprise first and second inputs to the fluidic system.

9. The fluidic isolation circuit set forth in claim 8 and further comprising means provided in said fourth and fifth passages for converting the single-sided pressure pulsation signal to a differential pressurized pulsating signal which is applied to the fluidic system.

10. The fluidic isolation circuit set forth in claim 9 wherein said converging means comprise:

a second fluidic resistor connected in said fourth passage;

and

a third fluidic resistor and a fluidic reactive element connected in said fifth passage for determining a time delay circuit, the frequency corresponding to the. time constant of the delay circuit being less than the minimum frequency of pressure pulsations inthe fluid pressure pulsation signal source to provide at the output ends of said fourth and fifth passages the pressure pulsation signal in differential pressurized form.

II. The fluidic isolation circuit set forth in claim 10 wherein said fluidic reactive element in a fluidic capacitor.

12. The fluidic isolation circuit set forth in claim 10 wherein said fluidic reactive element is a fluidic inductor.

13. The fluidic isolation circuit set forth in claim 10 wherein the resistance of said first resistor is less than the resistance of said second resistor.

14. The fluidic isolation circuit set forth in claim 10 wherein 

